实现字符串函数，strlen(),strcpy(),strcmp(),strcat()

#include<stdio.h>
#include<stdlib.h>

int my_strlen(char *str);
char *my_strcpy(char *dest, char *src);
char *my_strcat(char *dest, char *src);
int my_strcmp(char *str1,char *str2);

int main()
{
char dest[32] = "chen";
char src[32] = "chengha";
int res;
//printf("strlen(%s) = %d\n",str,my_strlen(str));
res = my_strcmp(dest,src);
printf("res = %d\n",res);
//puts(dest);
system("pause");
return 0;
}

int my_strlen(char *str)
{
int len = 0;
while(*str != '\0')
{
len++;
str++;
}
return len;
}

char *my_strcpy(char *dest, char *src)
{
char *address = dest;
while((*dest = *src) != '\0')
{
dest++;
src++;
}
return address;
}

char *my_strcat(char *dest, char *src)
{
char *address = dest;
while(*dest != '\0')
dest++;
while((*dest = *src) != '\0')
{
dest++;
src++;
}
return address;
}

int my_strcmp(char *str1,char *str2)
{
for(; *str1 == *str2; str1++, str2++)
if(*str1 == '\0')
return 0;
return *str1 - *str2;
}